This project addresses a number of issues related to cochlear implantation using electrophysiological techniques. Since we plan to implant children at very young ages, the issue of hearing assessment becomes important. Experiments using acoustic stimuli and the steady state evoked potential as a response measure will be used to address this issue. Once implanted, the limitations of behavioral testing in young children make the use of electrically evoked physiological responses a viable tool for determining appropriate parameters for stimulation. Experiments using electrical stimulation will assess the correlation between a variety of physiological measures and behaviorally determined programming levels. Once implanted, both adults and children display a wide range of abilities with the implant. We plan a series of experiments under Aim 4 that attempt to use physiological means to assess effective means of stimulation. In conjunction with the Audiology and Music projects will test the relationship to perceptual abilities. The implantation of individuals with significant residual hearing affords the opportunity to novel speech and music processing schemes as outlined in the Audiology and Music projects. Physiological experiments are planned which specifically measure the effects of functional hair cells on electrical stimulation of neurons and also the interaction of acoustic and electrical stimulation of the cochlea. These experiments are designed to assist in understanding the limitations of stimulation under these conditions as well as to suggest specific directions for signal processing parameter manipulations. Finally, the population of subjects with cochlear implants has been followed for as long as 15 years using a variety of physiological and perceptual measures. The longitudinal changes that take place as children mature into adults or as adults become older provide a unique opportunity to assess the source of such changes. Physiological data from the auditory periphery can serve as an important comparison to perceptual data collected as part of the Audiology and Music projects as well as language development and speech production data in children collected as part of the Language project.